Recently, use of a magnetic field for identification purposes has been very extensive and vital. This can be seen in a myriad of secured articles which utilize magnetic patterns or magnetic particles as their identification means. Some examples include security documents such as cheques, credit cards or tickets which typically use magnetic inks or magnetic strips for storing encrypted security information. Other examples include anti-counterfeit tags which use magnetic particles to create a random arrangement which acts as a magnetic fingerprint. In addition, magnetic barcodes and magnetic patterns are also gaining popularity as magnetic security features.
Using a magnetic field for identification is popular as it is an affordable form of a non-visible identification that can be read quickly and reliably. Besides, identification tags which use magnetic fields generally do not require any additional power to function as the magnetic field is an inherent feature of the magnetic materials.
However, means for detecting magnetic fields in the area of security features have been very limited. Most magnetic secured objects, in particular security cards and documents, commonly adopt a detection means which involves sliding the objects' magnetic face into a slot to obtain a magnetic signal. Nevertheless, increased security often requires the resolution of the magnetic field signal to a fine level. This encourages the development of new high-resolution detection means with improved usability for users.
An example of a high-resolution detection method is a magneto-optical detection. In the case of magneto-optical disks (for example Sony's “MiniDiscs”) and similar data storage devices, the magneto-optic detection is achieved by bouncing polarized light off the reflective surface inside the digital video disc (DVD). The polarization of the reflected light is changed due to the presence of a magnetic field at or around the reflective surface (generally this rotation of the polarization is due to the magneto-optic Kerr effect). By measuring the change in polarization, a detector is able to get a measure of the strength of the magnetic field at the reflective surface. This system works well for DVDs due to their form factor (for example they are very smooth and flat) and the fact that they are not generally subjected to harsh environments. However security labels and markings may be subjected to severe scratching and other harsh conditions during their service life. Therefore in the case of security labels and markings, it is not always practical to use a reading method which requires the substrate being read (for example the label) to contain a mirror-finish reflective surface.
Fortunately an alternative magneto-optic detection method exists. Here the reflective surface is part of the reading device itself and the light is reflected internally to the reading device itself. The reflective surface of the reading device is brought into close contact with substrate to be read such that the magnetic field from the substrate can influence the materials or light within the device. This means that the substrate being read is freed from the constraint of having to have a flat mirror surface. Other detection methods involve use of Giant Magnetoresistance (GMR), Flux concentrator for example.
Internally reflective magneto-optical readers have been developed by many groups for use in the field of storage devices but their usages for identification purposes are very limited. Some examples of magneto-optical readers are detailed below.
U.S. Pat. No. 3,512,866 discloses a magneto-optical hand viewer. The hand viewer is directed specifically to an apparatus constructed to operate using magneto-optical principles for providing a visual representation of magnetic states in a magnetic medium such as a magnetic tape. The hand viewer provides visual representation using the Kerr and Faraday magneto-optical effects. The Kerr magneto-optical effect produces a rotation of the major direction of polarization of the rays of a light beam reflected from a magnetic surface. The Faraday magneto-optical effect produces a rotation of the major direction of polarization of the rays of a light beam passing through a magnetic medium. The magneto-optical hand viewer uses a combination of the Kerr and Faraday magneto-optical effects to provide maximum amplitude of rotation of the rays of the light beam.
U.S. Pat. No. 5,742,036 discloses a method for marking, capturing and decoding machine-readable matrix symbols using magneto-optic imaging techniques. The patent involves enhancing machine-readable matrix symbol markings on substrate materials by the addition of magnetisable materials, and then, at a later time, taking advantage of the magnetic properties associated with the matrix symbol marking to read the marking using a magneto-optic reading apparatus. However, the method described in the patent mainly deals with the detection of Vericode® or other machine readable matrix symbols made by depositing a viscous magnetic compound. In addition, the patent describes the detection of a magnetic anti-counterfeit symbols, but it does not consider magneto-optics for use in non-symbology applications; for example for use imaging the inherent randomness of scattered magnetic particles. In other words, the magneto-optic reader in the patent recognizes symbols written with magnetic particles but does not read individual particles and considers their random position in a fixed area such that the area possesses a non-repeatable pattern in fine resolution.
U.S. Pat. No. 5,920,538 discloses a magneto-optical readout method for reading stored data, a magneto-optical readout head and a method for making the same. The patent describes a magneto-optical readout head for reading magnetically stored data for use with a source of illuminating light having a wavelength. The magnetic-optical readout head comprises an optically transparent substrate having a surface adapted to face a magnetic storage medium, an optically transparent Faraday effect rotator, having a Faraday coefficient θF disposed on said surface of said substrate and having a Faraday effect rotator surface adapted to face said magnetic storage medium and an optically reflective Kerr effect rotator having a Kerr coefficient θK disposed on said Faraday rotator surface, with θK and θF having a same operational sign at said wavelength of said illuminating light.
In the field of anti-counterfeit technology, it is also found that it is highly advantageous to use combinations of technologies for enhanced protection, for example, reading both magnetic data and optical data. Some examples of combined optical and magnetic transducers are as such.
U.S. Pat. No. 3,612,835 discloses a combined optical and magnetic transducer for sensing both optical and magnetic properties of an article, for example, a piece of paper currency or other document having both visible and magnetic markings to be tested or read, an information-bearing medium such as a data-recording tape to be read, or the like. The transducer comprises a magnetic-sensing head having a transparent gap separating the poles of the magnetic core of the head, a photoelectric element being disposed in the head in alignment with the gap. Outside the head, one side of the article contacts or is in close proximity to the poles at the gap, and the article is illuminated by a light source, so that both magnetic properties and optical properties of the article may be detected simultaneously during relative movement of the article and the transducer.
U.S. Pat. No. 3,876,981 discloses a character recognition system and method for recognizing characters printed in magnetic ink in which recognition is enhanced by sensing the characters with both magnetic and optical transducers. At least a signal derived from the magnetic transducer output signal is combined with at least a signal derived from the optical transducer output signal either at or prior to the recognition stage.
U.S. Pat. No. 6,745,942 discloses a magnetic symbology reader having a housing containing a polarized light source which directs light through a magneto-optic sensor onto a reflector which reflects light back through the magneto-optic sensor and then through at least one analyzer and into at least one camera. A view finder allows the user to monitor the image on the magneto-optic sensor as seen by a viewfinder camera while a processor is coupled to possibly a second camera so that when an image is detected, the image from the camera may be processed by the processor to output information associated with the symbol to an external source. The analyzer and polarized light source provide contrast in the images detected by the sensor. A bias or erase coil located about the magneto-optic sensor can enhance or erase images on the sensor.
One of the early usages of magnetically readable identification can be found in U.S. Pat. No. 3,755,730. U.S. Pat. No. 3,755,730 discloses a vehicle, appliance or tool having a multiplicity of magnetisable identifying indicia hidden by an opaque, protective layer such as paint. The indicia may be read by the use of a magnetic reader.
Another example is disclosed in PCT publication number WO 2004/013735. The publication discloses a system and an associated method providing a marking of material to be applied to goods. In one embodiment, magnetic material is applied in a predetermined pattern. An accumulation of magnetic material in one orientation across the structured pattern may provide an automatically sensible value. Magnetically readable material may be provided as a predetermined, repeatable pattern, where the magnetic material is applied to a surface with a resolution in a range of at least 10,000 to 100 dots per inch.
Further prior art on repeatable magnetic pattern on documents and articles of manufacture are described in the following:
U.S. Pat. No. 3,878,367 discloses a security document having a magnetic recording layer containing uniformly dispersed magnetisable material having magnetic anisotropy wherein the material at a plurality of selected locations is differently physically aligned with respect to a reference location to provide a magnetically detectable permanent fixed information pattern such as a code pattern useful for authenticating the document.
U.S. Pat. No. 4,081,132 discloses a security document having a carrier and two layers of magnetisable material, one overlying the other, the carrier and layers being all bonded together. One layer is for the recording of information and the other layer has a magnetic structure which can be examined for verification purposes. The patent discloses that a preferred method of making the structured layer is to deposit magnetisable material to form the layer within the influence of a magnetic field from a recording on the information layer which is of the form of the structure. The recording is erased when the structured layer has been formed. The security document may be a credit card, a bank note or other valuable paper.
U.S. Pat. No. 3,803,634 discloses an apparatus and a method for magnetic printing in which one or more perforations are formed in a base plate of a master magnetic medium for magnetic pattern printing, and one or more magnetizing elements formed illustratively of permanent magnets are disposed in the perforations with their end faces projecting a small distance from the surface of the base plate. The surface of a magnetic film of a slave magnetic medium for copying is contacted closely with the end faces of the magnetizing elements, and an external magnetic field is impressed to the contacted portions. The desired magnetic patterns are formed by the arrangement of the magnetizing elements or by the relative movement of said magnetizing elements with respect to the slave magnetic medium for copying; as a result, said magnetic patterns are copied on the magnetic film of the slave magnetic medium.
U.S. Pat. No. 4,183,989 discloses a security paper which contains a security device e.g. a strip, thread or planchette having at least two machine verifiable security features thereon, one of which is a magnetic material, which may be magnetically coded or printed in a predetermined pattern on the device, and a second of which is a luminescent material, an X-ray absorbent or a metal. The provision of several features on one device provides a large increase in document security.
U.S. Pat. No. 3,701,165 discloses garments which are formed with marks or stitching which carry a substance detectable by magnetic detecting devices. When the magnetized substance on the garment part is detected in a process of making garments, subsequent garment making steps are actuated in response to the detection of the stitching.
U.S. Pat. No. 4,180,207 discloses a secure document is produced by securely attaching to a support, a body including a security feature and having a shape which conveys information to the eye. For example the body is a layer of magnetisable material having apertures of letters, numbers and the like. The document can be examined by both magnetic and optical examination apparatus to cross-check that no alteration has been made. A method of making a secure document and examination apparatus is also described. The security feature may be a pattern of magnetic anisotropy fixed into the material.
U.S. Pat. No. 3,755,730 discloses a vehicle, appliance or tool having a multiplicity of magnetisable identifying indicia hidden by an opaque, protective layer such as paint. The indicia may be read by the use of a magnetic reader.
In creating the preferred anti-counterfeit magnetic fingerprints, magnetic particles need to be aligned in a particular manner to give distinguishable signals. One approach is disclosed in United States Patent Application Number 20060081151. The patent application discloses a method and apparatus for printing using paste like inks such as those used in intaglio printing, wherein the inks include specialty flakes such as thin film optically variable flakes, or diffractive flakes. The patent application also discloses an apparatus having an energy source such as a heat source for temporarily lessening the viscosity of the ink during alignment of the flakes within the ink.
A similar method can also be found in U.S. Pat. No. 7,047,883. U.S. Pat. No. 7,047,883 discloses an apparatus and related methods to align magnetic flakes in a carrier, such as an ink vehicle or a paint vehicle to create optically variable images in a high-speed, linear printing operation. Images can provide security features on high-value documents, such as bank notes. Magnetic flakes in the ink are aligned using magnets in a linear printing operation. Selected orientation of the magnetic pigment flakes can achieve a variety of illusive optical effects that are useful for decorative or security applications.
However there is still a need for a reading device, system and method for identifying tags or objects adapted to be identified which provides sufficient security of verification, i.e. in which the reliability of the identification is sufficiently high.
It is an objective of the present invention to provide such a reading device, system, and method. This objective, and others, is solved by the reading device, method and system as defined by the respective independent claims.